Conventional flexible connectors, e.g. vibration isolators, consist of resilient elements (made of rubber, plastic, cork, metal springs, etc.) which are placed between the unit being isolated and the support structure, or between structural components. Frequently, the connector is designed as a self-contained unit in which the resilient element is attached to input and output (e.g., top and bottom) covers, thus resulting in an easy to handle block. The connectors are characterized by their stiffness in the orthogonal coordinate directions (e.g. X, Y, and Z). While lower stiffness (and resulting low natural frequencies of the vibration isolation system) in some or all of these directions are desirable, they are associated with larger displacements under steady loads (e.g. weight load of the isolated object, tangential forces in flexible couplings, etc.) and larger excursions under dynamic loads (e.g., dynamic vibratory loads transmitted from road disturbances to an automotive engine isolated by engine mounts). Large displacements and excursions, together with large overall dimensions of flexible connectors in the directions of these displacements/excursions require increased space for packaging. Such space is frequently not available (e.g., in engine compartments of surface vehicles). This precludes use of the low stiffness flexible connectors, such as vibration isolators which otherwise would provide more effective isolation of unwanted vibrations.
In allocating the packaging space for the elastomeric flexible connectors, it is universally accepted that scatter of their hardness within .+-.5 units of Shore durometer (approximately .+-.17% in stiffness)is allowable in most cases.
Especially critical is the packaging problem for flexible connectors with elastomeric (rubber) resilient elements loaded in compression by the weight load of the supported unit. Such mode of loading allows, on one hand, to accommodate large weight and other steady loads with relatively small cross sections of the resilient elements. On the other hand, allowable continuous compression deformation of rubber blocks bonded to covers is 10-15% (e.g., see Shock and Vibration Handbook, ed. by C. Harris, 1987, McGraw-Hill, N.Y., Ch.35). It means that the dimension of the block in the direction of the weight or other steady load is 7-10 times larger than its steady-load induced deformation, which is often unacceptable or inconvenient.
Also, an increasing continuous (static) deformation of a resilient rubber block bonded to its covers and loaded in compression must be accompanied by increasing of its dimensions not only in the direction of compression but in the perpendicular directions as well, due to buckling considerations. This effect further increases the overall dimensions and weight of isolators.
If the bonded rubber block is subjected to intensive dynamic exertions causing significant excursions, the stresses associated with these excursions are amplified due to known stress concentrations at the bonded interfaces between the rubber block and the covers (especially, in the corners).
It is known that the use of streamlined rubber elements such as balls, ellipsoids, toruses, radially-loaded cylinders, etc., allows to significantly (two-three times) increase the allowable continuous compression deformation (e.g., see Kerr, M. L. and Schmitt, R. V., "A New Elastomeric Suspension Spring," SAE paper 710058, 1971). Another advantage of such streamlined elements is their progressively non-linear deformation characteristic. These improvements are due to absence of bonding and also due to specifics of stress distribution in such elements. However, bonding of the streamlined elements into an integrated system which is essential for utilization of flexible connectors in the machine design practice, would negate the noted advantages. Such compromise solution (spherical rubber elements with modified apexes bonded to the cover metal plates) was produced, for example, by Lord Corp. under the trade name "Lastoflex."
The present invention addresses the inadequacies of the prior art by providing a self-contained flexible connector using streamlined elastometric elements without compromising their special deformation properties, which may be caused by their bonding to other elements. The connector is composed of a single or a plurality of streamlined rubber elements, possibly in combination with hard material (e.g, metal) elements or differently shaped rubber elements (inserts) structurally integrated into a self-contained block by a soft matrix not influencing, to an undesirable degree, deformations of the resilient rubber element under static and/or dynamic loads. Appropriately shaped attachment and fastening features (such as holes, shaped corners, recesses, etc.) can be made in the matrix and/or in the inserts. The matrix can be made of a flexible foam or a solid (non-foamy) material which is significantly softer than the resilient elements. This arrangement eliminates influence of friction at the supporting surfaces on deformation of streamlined rubber elements and also results in a self-contained integrated block which is easy to handle and use in assemblies, while assuring the desired relative positions of the resilient elements and not creating any stress concentrations. Use of hard material inserts in this block allows to tailor the desired stiffness ratios in different coordinate directions; to reduce the overall dimensions while achieving high deformations under static loads; and to modify load deflection characteristics in various directions by an appropriate shaping of the inserts.